.Net: Sample image to text - Small fix (#5492)

### Motivation and Context

- ImageContent MimeType is not set in constructor, but in property.
- `ImageFormat` was not properly set when reading the File Stream.

dotnet/samples/HuggingFaceImageTextExample/FormMain.cs

@@ -143,21 +143,25 @@ private void UpdateImageDescription(string description)
     /// <param name="pictureBox">The target <see cref="PictureBox"/>.</param>
     /// <returns>Returns a <see cref="ImageContent"/>.</returns>
     private static ImageContent CreateImageContentFromPictureBox(PictureBox pictureBox)
-        => new(ConvertImageToReadOnlyMemory(pictureBox.Image))
+        => new(ConvertImageToReadOnlyMemory(pictureBox))
         {
             MimeType = GetMimeType(pictureBox.Tag?.ToString()!)
         };
 
     /// <summary>
-    /// Converts an <see cref="Image"/> to a <see cref="ReadOnlyMemory{T}"/>.
+    /// Gets the image binary array from a <see cref="PictureBox"/>.
     /// </summary>
-    /// <param name="image">The target <see cref="Image"/>.</param>
+    /// <param name="pictureBox">The target <see cref="PictureBox"/>.</param>
     /// <returns>Returns image binary array.</returns>
-    private static ReadOnlyMemory<byte> ConvertImageToReadOnlyMemory(Image image)
+    private static ReadOnlyMemory<byte> ConvertImageToReadOnlyMemory(PictureBox pictureBox)
     {
+        var image = pictureBox.Image;
+        var fileName = pictureBox.Tag.ToString()!;
+
         using var memoryStream = new MemoryStream();
+
         // Save the image to the MemoryStream, using PNG format for example
-        image.Save(memoryStream, ImageFormat.Jpeg);
+        image.Save(memoryStream, GetImageFormat(fileName));
 
         // Optionally, reset the position of the MemoryStream to the beginning
         memoryStream.Position = 0;
@@ -189,7 +193,22 @@ private static string GetMimeType(string fileName)
             ".tiff" => "image/tiff",
             ".ico" => "image/x-icon",
             ".svg" => "image/svg+xml",
-            _ => "application/octet-stream"
+            _ => throw new NotSupportedException("Unsupported image format.")
+        };
+    }
+
+    private static ImageFormat GetImageFormat(string fileName)
+    {
+        return Path.GetExtension(fileName) switch
+        {
+            ".jpg" or ".jpeg" => ImageFormat.Jpeg,
+            ".png" => ImageFormat.Png,
+            ".gif" => ImageFormat.Gif,
+            ".bmp" => ImageFormat.Bmp,
+            ".tiff" => ImageFormat.Tiff,
+            ".ico" => ImageFormat.Icon,
+            ".svg" => ImageFormat.MemoryBmp,
+            _ => throw new NotSupportedException("Unsupported image format.")
         };
     }
 

dotnet/samples/HuggingFaceImageTextExample/README.md

@@ -26,11 +26,11 @@ var service = this._kernel.GetRequiredService<IImageToTextService>();
 Once one of the images is selected, the binary data of the image is retrieved and sent to the ImageToText Service. The service then returns the descriptive text of the image. The following code snippet demonstrates how to use the ImageToText Service to retrieve the descriptive text of an image:
 
 ```csharp
-// Get the binary content of an image:
-var imageBinary = File.ReadAllBytes("path/to/file");
+// Get the binary content of a JPEG image:
+var imageBinary = File.ReadAllBytes("path/to/file.jpg");
 
 // Prepare the image to be sent to the LLM
-var imageContent = new ImageContent(imageBinary, "image/jpeg"));
+var imageContent = new ImageContent(imageBinary) { MimeType = "image/jpeg" };
 
 // Retrieves the image description
 var textContent = await service.GetTextContentAsync(imageContent);